Ambulatory medical devices include implantable medical devices (IMDs) and wearable medical devices (WMDs). Some examples of these implantable medical devices (IMDs) include cardiac function management (CFM) devices such as implantable pacemakers, implantable cardioverter defibrillators (ICDs), cardiac resynchronization therapy devices (CRTs), and devices that include a combination of such capabilities. The devices can be used to treat patients or subjects using electrical or other therapy or to aid a physician or caregiver in patient diagnosis through internal monitoring of a patient's condition. The devices may include one or more electrodes in communication with one or more sense amplifiers to monitor electrical heart activity within a patient, and often include one or more sensors to monitor one or more other internal patient parameters. Other examples of IMDs include implantable diagnostic devices, implantable drug delivery systems, or implantable devices with neural stimulation capability.
WMDs include wearable cardioverter defibrillators (WCDs) and wearable diagnostic devices (e.g., an ambulatory monitoring vest). WCDs can be monitoring devices that include surface electrodes. The surface electrodes are arranged to provide one or both of monitoring to provide surface electrocardiograms (ECGs) and delivering cardioverter and defibrillator shock therapy.
Some medical devices detect events by monitoring electrical heart activity signals. In CFM devices, these events can include electrical cardiac activity. By monitoring cardiac electrical signals, IMDs can detect abnormally slow heart rate, or bradycardia. Some IMDs detect abnormally rapid heart rate, or tachyarrhythmia. Tachyarrhythmia includes ventricular tachycardia (VT) and supraventricular tachycardia (SVT). Tachyarrhythmia also includes rapid and irregular heart rate, or fibrillation, including ventricular fibrillation (VF).
When detected, tachyarrhythmia can be terminated with high energy shock therapy using an ICD or WCD. Under-detection of tachyarrhythmia (i.e., the device does not recognize an episode of tachyarrhythmia) may leave tachyarrhythmia untreated. Additionally, over-detection of tachyarrhythmia by a device (i.e., the IMD categorizes too many false-positives as tachyarrhythmia) is undesirable for the patient and the device. Cardioversion/defibrillation therapy can cause patient discomfort and consumes a relatively large amount of battery power which may lead to a shortened useful device lifetime. Therefore, it is important to accurately detect tachyarrhythmia.